I've reloaded couple 1000 .40 and have never had this problem. I've seen this before and it looks to me like Bullet seated to deep/over Crimping/ over charge or something to cause a lot of case pressure. How hard do you have to pull the handle to seat the bullets? you shouldn't have to force it. Also stay away from MAX loads if possible. Going to the range for some family shooting isn't worth the catastrophe.